Phase-change self-degradation temporary plugging agent and preparation method thereof

Abstract

The invention discloses a phase change self-degradation temporary plugging agent which comprises the following components in parts by mass: 4-15 parts of a functional polymer solid; 5-70 parts of a functional solvent; 10 to 80 parts of water; the invention further discloses a preparation method of the phase-change self-degradation temporary plugging agent, the phase-change self-degradation temporary plugging agent is suitable for the technical fields of oilfield chemistry and colloidal chemistry, and compared with particle and fiber temporary plugging agents, the phase-change self-degradation temporary plugging agent has the advantages that the pore throat size does not need to be considered, and broad-spectrum plugging can be realized; compared with a conventional gel temporary plugging agent needing additional plug removal, the temporary plugging agent can be subjected to in-situ self-degradation plug removal in a reservoir; the temperature window is large, the phase transition time is adjustable, meanwhile, the plugging agent has the characteristics of broad-spectrum plugging and self-degradation plugging removal, the actual production requirement can be met, and the green mining policy can be implemented.

Description

Technical Field

[0001] The present invention belongs to the technical fields of oilfield chemistry and colloid chemistry, and specifically relates to a phase-change self-degrading temporary plugging agent and a preparation method thereof. Background Art

[0002] The temporary plugging agent is also called a diversion agent or a shielding agent. The temporary plugging operation generally refers to injecting the temporary plugging agent in advance before injecting the well fluid to achieve the plugging of the formation pore throats. After the operation is completed, based on the dissolution performance or degradation performance of the temporary plugging system, the plugging is removed by reverse dissolution to restore the seepage characteristics of the reservoir. During operations such as drilling and well completion, fluid loss and reservoir damage are likely to occur, causing an economic loss of approximately $1 billion worldwide each year. The temporary plugging operation can form a surface shield, effectively prevent fluid loss, and protect the reservoir. For fracturing operations, the temporary plugging operation can reduce pressure loss, improve the fracturing fracture formation efficiency, and create a larger oil drainage area. For acidizing operations, temporary plugging acidizing can avoid waste, achieve uniform acid distribution, and targeted acid injection. The temporary plugging operation has an obvious promoting effect on reservoir protection, reservoir transformation, and increasing oil and gas production. Therefore, the development of temporary plugging agents has become a research hotspot in the field of oil and gas development for production enhancement.

[0003] The temporary plugging agent was first reported by Halliburton in 1936, and an oil-soluble calcium compound type temporary plugging agent was prepared based on the reaction of fatty acid salts and calcium chloride. Developed to date, the temporary plugging modes are mainly divided into two categories, namely mechanical temporary plugging and chemical temporary plugging. Mechanical temporary plugging has high costs and cumbersome operations. In comparison, the chemical temporary plugging process is simple, low-cost, and can directly act on the formation pore throats. Therefore, it has greater application potential in the process of oil and gas exploitation. Among chemical temporary plugging agents, the most widely applied and studied are particulate, fibrous, and compound temporary plugging agents. The temporary plugging mechanisms of these three types are relatively consistent, that is, they first enter the interior of the formation pore throats with the assistance of the carrying fluid, and form a slug shield based on the bridging rule, or capture fibers on the throat wall surface to form a filter cake for plugging. After the downhole operation is completed, the reservoir permeability is restored by water dissolution, oil dissolution, or degradation. However, the severe reservoir heterogeneity, wide distribution of formation pore throats, and difficult accurate measurement of pore throat sizes lead to poor matching between the temporary plugging agent and the pore throats, weakening the plugging strength and effectiveness, and restricting its application scope. Therefore, developing a temporary plugging agent that does not require prior knowledge of pore throat sizes and can achieve broad-spectrum plugging is more in line with the development trend of oil and gas exploitation and meets the application requirements.

[0004] The currently reported gel temporary plugging agents can achieve broad-spectrum plugging, and their action mechanism is as follows: The functional polymer and the cross-linking agent are dissolved in water to form a solution with low viscosity and strong fluidity, which is pumped into the formation target pore throats in a slug manner to cross-link and form a gel plugging layer, achieving broad-spectrum plugging of reservoirs with different sizes of pore throats.

[0005] The existing types of gel temporary plugging agents mainly include:

[0006] (1) Polyvinyl alcohol and boric acid system;

[0007] (2) Polyacrylamide and polyethyleneimine system. In 2018, Almuntassheri G [Gelation Kinetics and Performance Evaluation of an Organically Crosslinked Gel at High Temperature and Pressure [J]. Spe. Journal] used polyethyleneimine (PEI) as an organic crosslinking agent for polyacrylamide-based (PAM) copolymers to prepare a thermally stable gel temporary plugging agent. However, the crosslinking of PAM and PEI at a temperature of 130 °C requires at least 8 weeks to obtain a thermally stable gel, and the time required to achieve temporary plugging is relatively long, which is not conducive to the temporary plugging operation. Moreover, peroxide is needed for gel breaking and plug removal, and it is easy to have incomplete plug removal.

[0008] (3) Partially hydrolyzed polyacrylamide and high-valent metal ion system. In 2016, Zhao G [Research on a temporary plugging agent based on polymer gel for reservoir acidification [J]. Journal of Petroleum Exploration & Production Technology] used an environmentally friendly organic chromium crosslinking agent and anionic polyacrylamide as raw materials, and introduced ammonium persulfate (APS) to develop a temporary plugging agent for acidification based on polymer gel. This temporary plugging agent has the advantage of low cost, but the plug removal is incomplete, and there is still a certain degree of secondary damage to the formation after plug removal.

[0009] (4) Polyacrylamide and phenolic crosslinking agent system, etc. However, conventional gel temporary plugging agents are not easy to remove plugs. Peroxide-based gel-breaking agents such as ammonium sulfate and hydrogen peroxide need to be injected for plug removal. For gels in the far wellbore zone, the plugs cannot be completely removed, which is easy to cause reservoir damage. Moreover, this gel-breaking agent is easy to corrode the wellbore and casing, affecting downhole operations.

[0010] Aiming at the problems existing in the practical application of conventional temporary plugging agents, such as the difficulty in matching with pore throat size and the need for additional plug removal operations and other application limitations, it is urgent to develop a temporary plugging system that simultaneously has broad-spectrum plugging and self-degrading plug removal, that is, a temporary plugging agent based on phase change self-degradation, which is of great significance for meeting the actual production needs and implementing the "green mining" policy. Summary of the Invention

[0011] The purpose of the present invention is to overcome the defects of the prior art and provide a phase change self-degrading temporary plugging agent and its preparation method.

[0012] To achieve the above purpose, the present invention adopts the following technical solutions:

[0013] In a first aspect, a phase change self-degrading temporary plugging agent comprises the following components by mass fraction:

[0014] 4 to 15 parts of a functional polymer solid;

[0015] 5 to 70 parts of a functional solvent;

[0016] 10 to 80 parts of water;

[0017] 1 to 40 parts of a crosslinking agent.

[0018] Preferably, the functional polymer solid comprises the following components by mass fraction:

[0019] 12 to 34 parts of monomer small molecules;

[0020] 66 to 88 parts of a functional solvent;

[0021] 0 to 50 parts of water;

[0022] 0.08 to 0.8 parts of an initiator.

[0023] Preferably, the functional polymer solid is one of functional polymers such as poly-4-hydroxybutyl acrylate, poly(2-hydroxypropyl methacrylate), poly(isocyanoethyl methacrylate), poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl methacrylamide), poly(2-hydroxypropyl methacrylate), poly(2-hydroxypropyl methacrylamide), poly(2-hydroxyethyl phenyl methacrylate), poly(2-aminoethyl methacrylate), poly(2-methylaminoethyl methacrylate).

[0024] Preferably, the initiator is one or more of benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, sodium bisulfite, ammonium persulfate, potassium sulfite, sodium persulfate, potassium persulfate, azobisisobutyronitrile, azobis(isovaleric acid).

[0025] Preferably, the functional solvent is one or several of acetone, carbon tetrachloride, N,N-dimethylformamide, cyclohexane, ethanol, ether, dimethyl sulfoxide or tetrahydrofuran.

[0026] Preferably, the water is deionized water or brine with a concentration of 0.5 wt% to 5 wt%.

[0027] Preferably, the water is one of 5 wt% sodium chloride brine, 4 wt% sodium chloride brine, 3 wt% sodium chloride brine, 2 wt% sodium chloride brine, 1 wt% sodium chloride brine and 0.5 wt% sodium chloride brine.

[0028] Preferably, the crosslinking agent is one or more of boric acid, diboric acid, 3-hydroxybenzeneboronic acid.

[0029] Preferably, the functional polymer solid is prepared by the following reaction:

[0030]

[0031] In a second aspect, a method for preparing a phase change self-degrading temporary plugging agent includes the following steps:

[0032] S1 Preparation of the functional polymer: Stir the monomer small molecules, functional solvent, water and initiator in the formula amount to obtain a functional polymer solution, precipitate the polymer, and dry it to obtain a functional polymer solid;

[0033] S2 Construction of the phase change self-degrading temporary plugging agent: Stir the functional polymer solid, functional solvent, water and cross-linking agent in the formula amount to obtain an initial solution of the broad-spectrum temporary plugging agent, then heat for a period of time, and spontaneously form a solution-gel transition based on the functional group reaction. Keep the temperature unchanged, and then heat for another period of time, and the gel self-degrades and breaks into a solution state to obtain the phase change self-degrading temporary plugging agent.

[0034] Preferably, in step S1, it specifically includes:

[0035] The dosage of the monomer small molecules, stirring speed, water dosage, initiator dosage and temperature are limited to enable the polymerization of the monomer small molecules.

[0036] Preferably, in step S1, the temperature is 30°C to 90°C, the stirring speed is 150 to 1100 rpm, and the stirring time is 1.5 to 10 h.

[0037] Preferably, in step S1, deionized water is used to precipitate the polymer.

[0038] Preferably, in step S2, the stirring speed and stirring time are limited to enable the formation of a homogeneous phase in the corresponding mixed system.

[0039] Preferably, in step S2, the reaction vessel is a sample bottle, and stirring is carried out by a magnetic stirrer and heating is carried out by an oven.

[0040] Preferably, in step S2, the stirring speed is 800 to 8000 rpm, and the stirring time is 0.2 to 2 h.

[0041] Preferably, in step S2, the heating temperature is 45 to 150°C, and the heating time is 0.5 to 100 h.

[0042] Preferably, in step S2, the re-heating time is 8 to 800 h.

[0043] Preferably, it further includes:

[0044] S3 Core Temporary Plugging Experiment: The temporary plugging performance was tested using a core displacement device. First, the core was cleaned with a 4 wt% KCl solution and then dried at 130 °C.

[0045] After drying, the core was placed in a core holder, and the temperature was set to 85 °C. The pre-gelled temporary plugging agent solution was injected into the core and allowed to stand. At regular intervals, the change in the plugging pressure was measured by injecting a 4 wt% KCl solution; the plugging rate and the unplugging rate of the core were calculated based on the pressure change.

[0046] Among them, the injection rate of all liquids was 6 mL / min.

[0047] Preferably, the core in step S3 is one of an artificial sandstone core, an artificial shale core, an artificial carbonate rock core, and a natural core, and its specifications are L×φ = 5.0 cm×2.5 cm.

[0048] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0049] In the present invention, compared with particle and fiber temporary plugging agents, broad-spectrum plugging can be achieved without considering pore throat size; compared with conventional gel temporary plugging agents that require additional unplugging, the temporary plugging agent involved can be self-degraded in situ in the reservoir for unplugging; it has a large temperature window, adjustable phase transition time, and simultaneously has the characteristics of broad-spectrum plugging and self-degrading unplugging, which can meet the actual production needs and implement the "green mining" policy. Description of the Drawings

[0050] Figure 1 is the gel chromatography spectrum of poly(4-hydroxybutyl acrylate) related to Example 1;

[0051] Figure 2 is the viscosity change during the solution-gel-solution transition of the phase change self-degrading temporary plugging system related to Example 1;

[0052] Figure 3 is the viscosity change during the solution-gel-solution transition of the phase change self-degrading temporary plugging system related to Example 2;

[0053] Figure 4 is the viscosity change during the solution-gel-solution transition of the phase change self-degrading temporary plugging system related to Example 3;

[0054] Figure 5 is the scanning electron microscope of the initial solution of Example 3;

[0055] Figure 6 is the scanning electron microscope of the gelled state after gel formation in Example 3;

[0056] Figure 7 is the scanning electron microscope of the solution after degradation in Example 3;

[0057] Figure 8 Viscosity variation with time during gelation and degradation in Example 5;

[0058] Figure 9 Temporary plugging performance curve of Example 6;

[0059] Figure 10 Flow chart for preparing phase change self-degrading temporary plugging agent;

[0060] Figure 11 Flow chart for core temporary plugging experiment. Specific embodiments

[0061] The following further illustrates the specific embodiments of a phase change self-degrading temporary plugging agent and its preparation method according to the present invention in conjunction with examples. The phase change self-degrading temporary plugging agent and its preparation method of the present invention are not limited to the descriptions of the following examples.

[0062] Example 1:

[0063] A phase change self-degrading temporary plugging agent and its preparation method, comprising the following steps:

[0064] (1) Weigh 24 g of 4-hydroxybutyl acrylate monomer, mix it evenly in 100 g of DMF, transfer it to a 250 mL three-necked flask, stir for 10 min, then add 0.3 g of benzoyl peroxide powder at 70 °C, and then raise the temperature to 80 °C. After reacting for 8 h, poly(4-hydroxybutyl acrylate) is obtained. Then, the polymer solid is precipitated by deionized water sedimentation and dried for standby. The gel chromatography results of this polymer are as Figure 1 shown, its weight average molecular weight is 2,521,154, and the PDI is 1.679, confirming its successful polymerization.

[0065] (2) Blend 0.04 g of the polymer prepared in step (1), 0.040 g of diboronic acid, and 4.50 g of DMF by magnetic stirring to form a homogeneous system. The stirring speed is 1000 rpm, and the stirring time is 10 min. Then, it is placed in a blast drying oven at 85 °C and left standing. Observe its changes at regular intervals. It can be seen that the gel strength reaches the maximum after 0.6 h. Keeping the oven temperature unchanged and continuing to stand for 40 h, degradation occurs and it returns to the solution state again. The viscosity change during the solution-gel-solution transition process is as Figure 2 shown. In this system at 85 °C, the initial viscosity is only 21 mPa·s. After heating, the viscosity continuously increases and reaches the peak of 24,000 mPa·s at 36 min. After continuing to heat, the viscosity starts to decrease, and after 40 h, it returns to the low-viscosity state. After complete degradation, the viscosity is only 25 mPa·s.

[0066] Example 2:

[0067] This embodiment discloses a phase-change self-degrading temporary plugging agent and its preparation method, including the following steps:

[0068] Increase the content of the cross-linking agent diboronic acid in Example 1 from 0.04 g to 0.05 g, and keep the others unchanged to form a homogeneous and stable solution. Put it into a blast drying oven at 85 °C for 40 min to form a gel, and continue to maintain this temperature for 45 h. Then the gel is completely degraded and becomes a solution with good fluidity. The viscosity change during the solution-gel-solution transformation process is as Figure 3 shown, where the viscosity increases to a maximum of 26,400 mPa·s, and the viscosity after degradation is still about 24 mPa·s.

[0069] Example 3:

[0070] This embodiment discloses a phase-change self-degrading temporary plugging agent and its preparation method, including the following steps:

[0071] Increase the content of the cross-linking agent diboronic acid in Example 1 from 0.04 g to 0.06 g, and keep the others unchanged to form a homogeneous and stable solution. Put it into a blast drying oven at 85 °C for 40 min to form a gel that cannot be shaken. Continue to maintain this temperature for 60 h. Then the gel is completely degraded and becomes a solution with good fluidity. The viscosity change during the solution-gel-solution transformation process is as Figure 4 shown, where the viscosity increases to a maximum of 31,000 mPa·s, and the viscosity after degradation is still about 32 mPa·s; during the solution-gel-solution transformation process of the system, the microscopic morphology is observed by scanning electron microscopy. Figure 5 is the liquid film morphology in the initial solution state, Figure 6 is the gel state after gel formation, Figure 7 is the liquid film state after degradation.

[0072] Example 4:

[0073] Experiment on the influence of temperature on gelation time, gel strength and gel-breaking time, including the following steps:

[0074] Blend 0.02 g of the polymer prepared in step (1) of Example 1, 0.04 g of diboronic acid and 4.50 g of DMF, and stir magnetically to form a homogeneous system. The stirring speed is 1000 rpm and the stirring time is 10 min. Conduct gelation and gel-breaking experiments at 45 °C, 65 °C, 85 °C, 105 °C and 125 °C respectively. As the temperature increases, the gelation times are 2 h, 1 h, 0.6 h, 0.5 h, 0.2 h respectively, and the corresponding gel-breaking times are 100 h, 60 h, 40 h, 20 h, 5 h. Temperature will accelerate the gelation and gel-breaking rates, and it is completely degraded in 5 h at high temperature, while the gel strength of the whole system is less affected by temperature.

[0075] Example 5:

[0076] This embodiment discloses a phase change self-degrading temporary plugging agent and its preparation method, including the following steps:

[0077] (1) Weigh 30 g of hydroxypropyl methacrylate monomer, mix it evenly in 100 g of DMF, transfer it to a 250 mL three-necked flask, stir for 10 min, then add 0.25 g of azobisisobutyronitrile at 70 °C, then raise the temperature to 80 °C, and prepare polyhydroxypropyl methacrylate after reacting for 8 h. Then, precipitate the polymer solid with deionized water and dry it for standby.

[0078] (2) Blend 0.05 g of the polymer prepared in step (1), 0.05 g of boric acid, and 4.50 g of DMF and stir magnetically to form a homogeneous system. The stirring speed is 1000 rpm, and the stirring time is 10 min to obtain a homogeneous solution. Put it into a blast drying oven at 85 °C for 40 min to form a gel, and continue to maintain this temperature for 80 h until the gel is completely degraded and becomes a solution with good fluidity. The viscosity changes with time during the gel formation and degradation processes as Figure 8 shown. At 85 °C, the viscosity of this system gradually increases with time, increasing from an initial 12 mPa·s to 46000 mPa·s. After maintaining this temperature for 80 h, the viscosity of the system gradually drops to 24 mPa·s, indicating complete gel breaking.

[0079] Example 6:

[0080] Blend 0.2 g of the polymer prepared in step (1) of Example 1, 0.6 g of diborinic acid, and 45 g of DMF and stir magnetically to form a homogeneous system. The stirring speed is 1000 rpm, and the stirring time is 10 min to form a temporary plugging fluid. Control the temperature at 85 °C, and select a fractured core as the test core. The results are as Figure 9 shown. In the initial stage, use KCl solution as the injection agent to measure the initial injection pressure of 0.08 MPa. Then, replace it with the temporary plugging fluid. After injecting 5 PV, close the injection device and let it stand for 1 h. Then, use KCl solution to measure the breakthrough pressure of 24 MPa, and then stabilize at 18 MPa. After 60 h, it degrades and returns to 0.1 MPa. The core plugging rate is greater than 99%, and the plug removal effect is good.

[0081] Example 7:

[0082] 0.2 g of the polymer prepared in step (1) of Example 5, 0.5 g of boric acid and 40 g of DMF were blended and magnetically stirred to form a homogeneous system at a stirring speed of 1000 rpm for 10 min to form a temporary plugging fluid. The temperature was controlled at 85 °C, and a fractured core was selected as the test core. In the initial stage, a KCl solution was used as the injection agent to measure an initial injection pressure of 0.09 MPa, and then it was replaced with the temporary plugging fluid. After injecting 3 PV, the injection device was closed and left standing for 50 minutes, and then the KCl solution was injected. The breakthrough pressure was measured to be 37 MPa and then stabilized at 30 MPa. After 80 h, it degraded and recovered to 0.12 MPa, and the core plugging rate was greater than 99%, and the plugging removal effect was good.

[0083] Example 8:

[0084] A preparation method of a phase change self-degrading temporary plugging agent, comprising the following steps:

[0085] (1) Preparation of a functional polymer. 12 parts by mass of monomer small molecules, 66 parts by mass of functional solvents, 0 parts by mass of water and 0.08 parts by mass of initiator were stirred at a temperature of 30 °C and a speed of 150 rpm for 1.5 h to obtain a functional polymer solution, and the polymer was precipitated with deionized water and dried to obtain a functional polymer solid.

[0086] The reaction process is as follows:

[0087]

[0088] (2) Construction of a phase change self-degrading temporary plugging agent. As Figure 10 shown, 4 parts by mass of the polymer solid prepared in step (1), 5 parts by mass of functional solvents, 10 parts by mass of water, and 1 part by mass of cross-linking agent were placed in a sample bottle and stirred on a magnetic stirrer at a rotation speed of 800 rpm for 0.2 h to obtain an initial solution of a broad-spectrum temporary plugging agent. Then it was left standing in an oven at 45 °C for 0.5 h, and a solution-gel transition occurred spontaneously based on the reaction of functional groups. The temperature was kept constant, and after 8 h, the gel self-degraded and broke down into a solution state. The solution-gel-solution transition was completed at a constant temperature, meeting the performance requirements of the degradable broad-spectrum temporary plugging agent.

[0089] Furthermore, the polymer is one of functional polymers such as poly-4-hydroxybutyl acrylate, polyhydroxypropyl methacrylate, polyisocyanoethyl methacrylate, polyhydroxyethyl methacrylate, polyhydroxyethyl methacrylamide, polyhydroxypropyl methacrylate, polyhydroxypropyl methacrylamide, polyphenol hydroxyethyl methacrylate, poly-2-aminoethyl methacrylate, poly-2-methylaminoethyl methacrylate, etc. The initiator is one of benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, sodium bisulfite, ammonium persulfate, potassium sulfite, sodium persulfate, potassium persulfate, azobisisobutyronitrile, azobis(isovaleric acid).

[0090] Further, the functional solvent is one of acetone, carbon tetrachloride, N,N-dimethylformamide (DMF), cyclohexane, ethanol, ether, dimethyl sulfoxide or tetrahydrofuran.

[0091] Further, the water is one of deionized water, 5wt% sodium chloride brine, 4wt% sodium chloride brine, 3wt% sodium chloride brine, 2wt% sodium chloride brine, 1wt% sodium chloride brine and 0.5wt% sodium chloride brine.

[0092] Further, the crosslinking agent is one of boric acid, diboronic acid or 3-hydroxybenzeneboronic acid.

[0093] Further, the dosage of monomer small molecules, stirring speed, water dosage, initiator dosage and temperature are limited to enable the polymerization of monomer small molecules.

[0094] Further, the stirring speed and stirring time are limited to enable the corresponding mixed system to form a homogeneous phase.

[0095] Example 9:

[0096] A phase change self-degrading temporary plugging agent and its preparation method, comprising the following steps:

[0097] (1) Preparation of the functional polymer. 23 parts by mass of monomer small molecules, 77 parts by mass of functional solvent, 25 parts by mass of water and 0.4 parts by mass of initiator are stirred at a temperature of 60 °C and a speed of 525 rpm for 6 h to obtain a functional polymer solution, and the polymer is precipitated and dried with deionized water to obtain a functional polymer solid.

[0098] The reaction process is as follows:

[0099]

[0100] (2) Construction of the phase change self-degrading temporary plugging agent. As Figure 10 shown, 10 parts by mass of the polymer solid prepared in step (1), 37 parts by mass of functional solvent, 45 parts by mass of water, and 20 parts by mass of crosslinking agent are placed in a sample bottle and stirred on a magnetic stirrer at a speed of 4400 rpm for 1.1 h to obtain an initial solution of the broad-spectrum temporary plugging agent. Then it is left standing in an oven at 100 °C for 50 h, and a solution-gel transition occurs spontaneously based on the functional group reaction. The temperature is maintained unchanged, and after 404 h, the gel self-degrades and breaks into a solution state. The solution-gel-solution transition is completed at a constant temperature, meeting the performance requirements of the degradable broad-spectrum temporary plugging agent.

[0101] Further, the polymer is one of functional polymers such as poly-4-hydroxybutyl acrylate, poly(2-hydroxypropyl methacrylate), poly(isocyanatoethyl methacrylate), poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl methacrylamide), poly(2-hydroxypropyl methacrylate), poly(2-hydroxypropyl methacrylamide), poly(phenoxyethyl methacrylate), poly(2-aminoethyl methacrylate), poly(2-(methylamino)ethyl methacrylate). The initiator is benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, sodium bisulfite, ammonium persulfate, potassium sulfite, sodium persulfate, potassium persulfate, 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile).

[0102] Further, the functional solvent is acetone, carbon tetrachloride, N,N-dimethylformamide (DMF), cyclohexane, ethanol, ether, dimethyl sulfoxide or tetrahydrofuran.

[0103] Further, the water is deionized water, 5wt% sodium chloride brine, 4wt% sodium chloride brine, 3wt% sodium chloride brine, 2wt% sodium chloride brine, 1wt% sodium chloride brine and 0.5wt% sodium chloride brine.

[0104] Further, the crosslinking agent is boric acid or diboronic acid, 3-hydroxybenzeneboronic acid.

[0105] Further, the dosage of monomer small molecules, stirring speed, water dosage, initiator dosage and temperature are limited to enable the polymerization of monomer small molecules.

[0106] Further, the stirring speed and stirring time are limited to enable the formation of a homogeneous phase in the corresponding mixed system.

[0107] Example 10:

[0108] A phase change self-degrading temporary plugging agent and its preparation method, comprising the following steps:

[0109] (1) Preparation of the functional polymer. 34 parts by mass of monomer small molecules, 88 parts by mass of functional solvent, 50 parts by mass of water and 0.8 part by mass of initiator are stirred at a temperature of 90 °C and a speed of 1100 rpm for 10 h to obtain a functional polymer solution, and the polymer is precipitated and dried with deionized water to obtain a functional polymer solid.

[0110] The reaction process is as follows:

[0111]

[0112] (2) Construction of the phase change self-degrading temporary plugging agent. As Figure 10As shown in the figure, 15 parts by mass of the polymer solid prepared in step (1), 70 parts by mass of the functional solvent, 80 parts by mass of water, and 40 parts by mass of the crosslinking agent are placed in a sample bottle. After stirring on a magnetic stirrer at a speed of 8000 rpm for 2 h, an initial solution of the broad-spectrum temporary plugging agent is obtained. Then it is left standing in an oven at 150 °C for 100 h, and a solution-gel transition occurs spontaneously based on the reaction of functional groups. The temperature is maintained unchanged, and after 800 h, the gel degrades and breaks through self-degradation and transforms into a solution state. The solution-gel-solution transition is completed at a constant temperature, meeting the performance requirements of the degradable broad-spectrum temporary plugging agent.

[0113] Furthermore, the polymer is one of functional polymers such as poly-4-hydroxybutyl acrylate, poly(2-hydroxypropyl methacrylate), poly(isocyanatoethyl methacrylate), poly(2-hydroxyethyl methacrylate), poly(2-hydroxyethyl methacrylamide), poly(2-hydroxypropyl methacrylate), poly(2-hydroxypropyl methacrylamide), poly(2-hydroxyethyl phenyl methacrylate), poly(2-aminoethyl methacrylate), poly(2-methylaminoethyl methacrylate). The initiator is benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, sodium bisulfite, ammonium persulfate, potassium sulfite, sodium persulfate, potassium persulfate, 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile).

[0114] Furthermore, the functional solvent is acetone, carbon tetrachloride, N,N-dimethylformamide (DMF), cyclohexane, ethanol, ether, dimethyl sulfoxide or tetrahydrofuran.

[0115] Furthermore, the water is deionized water, 5 wt% sodium chloride brine, 4 wt% sodium chloride brine, 3 wt% sodium chloride brine, 2 wt% sodium chloride brine, 1 wt% sodium chloride brine, and 0.5 wt% sodium chloride brine.

[0116] Furthermore, the crosslinking agent is boric acid or diboronic acid, 3-hydroxybenzeneboronic acid.

[0117] Furthermore, the dosage of monomer small molecules, stirring speed, water dosage, initiator dosage, and temperature are limited to enable the polymerization of monomer small molecules.

[0118] Furthermore, the stirring speed and stirring time are limited to enable the formation of a homogeneous phase in the corresponding mixed system.

[0119] Example 11:

[0120] Core temporary plugging experiment: As Figure 11As shown, a temporary plugging performance test was carried out using a core displacement device. First, an artificial sandstone core (L×φ = 5.0 cm×2.5 cm) was cleaned with a 4 wt% KCl solution, and then dried at 130 °C. The dried core was placed in a core holder, and the temperature was set to 85 °C. The pre-gelled temporary plugging agent solution was injected into the core and allowed to stand. At regular intervals, the change in the plugging pressure was measured by injecting a 4 wt% KCl solution. The core permeability at different time intervals was calculated using Darcy's formula, and the plugging rate and the unplugging rate of the core were calculated based on the pressure changes before and after plugging and before and after unplugging. The injection rate of all liquids was 6 mL / min.

[0121] Among them, the core is one of an artificial sandstone core, an artificial shale core, an artificial carbonate rock core, and a natural core.

[0122] Comparative Example 1:

[0123] 0.02 g of the poly(4-hydroxybutyl acrylate) solid prepared in step (1) of Example 1 and 4.50 g of dimethylformamide (DMF) were taken and blended and magnetically stirred to form a homogeneous system at a stirring speed of 1000 rpm for 10 min. Then it was placed in a forced-air drying oven at 85 °C and allowed to stand. There was no obvious change in the viscosity of the system within 2 days, and no gel was formed. It was confirmed that poly(4-hydroxybutyl acrylate) and dimethylformamide could not undergo a crosslinking reaction.

[0124] Comparative Example 2:

[0125] 0.04 g of diboronic acid and 4.50 g of dimethylformamide (DMF) were taken and blended and magnetically stirred to form a homogeneous system at a stirring speed of 1000 rpm for 10 min. Then it was placed in a forced-air drying oven at 85 °C and allowed to stand. There was no obvious change in the viscosity of the system within 2 days, and no gel was formed. It was confirmed that diboronic acid and dimethylformamide could not undergo a crosslinking reaction.

[0126] Comparative Example 3:

[0127] Temporary plugging performance test of a fibrous temporary plugging agent. Polyvinyl alcohol fiber temporary plugging agent was taken, with fiber size of 100 - 1000 microns, and blended with water and magnetically stirred to form a homogeneous system at a stirring speed of 1000 rpm for 10 min. A stable dispersion was formed as the fibrous temporary plugging system. A fractured core was selected as the test core. At the initial stage, KCl solution was used as the injection agent to measure the initial injection pressure of 0.08 MPa. Then the fiber temporary plugging agent was replaced, and after injecting 5 PV, the injection device was closed and allowed to stand for 2 h. Then the breakthrough pressure was measured with KCl solution to be 1.5 MPa, and it stabilized at 0.8 MPa later. The temporary plugging strength was weak, lower than that of Example 6 and Example 7, and the plugging rate was low.

[0128] Comparative Example 4:

[0129] Testing the temporary plugging performance of particulate temporary plugging agents. Take polylactic acid particulate temporary plugging agents with particle sizes ranging from 100 microns to 10 millimeters, blend them with water and stir magnetically to form a homogeneous system at a stirring speed of 1000 rpm for 10 minutes. A stable dispersion is formed as the particulate temporary plugging system. Select fractured cores as the test cores. In the initial stage, use KCl solution as the injection agent to measure the initial injection pressure of 0.08 MPa. Then replace it with the particulate temporary plugging agent. After injecting 5 PV, close the injection device and let it stand for 2 hours. Then use KCl solution to measure the breakthrough pressure of 1.2 MPa, and it stabilizes at 0.5 MPa later. The plugging strength is weak and the plugging rate is low, lower than that of the self-degrading temporary plugging agent systems in Example 6 and Example 7.

[0130] From the experimental results of the examples, it can be concluded that the homogeneous solution formed by one-step blending of polymers, cross-linking agents, and regulators has excellent solution-gel-solution transition properties, can have a certain temperature and salinity change window, and the core plugging experiment shows that it can plug and unplug artificial cores, having potential for field application.

[0131] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, which should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A phase change self-degrading temporary plugging agent, characterized in that, Comprising the following components by mass fraction: 4 - 15 parts of functional polymer solid; 5 - 70 parts of functional solvent; 10 - 80 parts of water; 1 - 40 parts of crosslinking agent.

2. The phase change self-degrading temporary plugging agent according to claim 1, characterized in that, The functional polymer solid, comprising the following components by mass fraction: 12 - 34 parts of monomer small molecule; 66 - 88 parts of functional solvent; 0 - 50 parts of water; 0.08 - 0.8 parts of initiator.

3. The phase change self-degrading temporary plugging agent according to claim 1, characterized in that, The functional polymer solid is one of functional polymers such as poly-4-hydroxybutyl acrylate, poly(hydroxypropyl methacrylate), poly(isocyanatoethyl methacrylate), poly(hydroxyethyl methacrylate), poly(hydroxyethyl methacrylamide), poly(hydroxypropyl methacrylate), poly(hydroxypropyl methacrylamide), poly(phenol hydroxyethyl methacrylate), poly(2-aminoethyl methacrylate), poly(2-methylaminoethyl methacrylate), etc.

4. The phase change self-degrading temporary plugging agent according to claim 2, characterized in that, The initiator is one or more of benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, sodium bisulfite, ammonium persulfate, potassium sulfite, sodium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisovaleric acid.

5. The phase change self-degrading temporary plugging agent according to any one of claims 1 or 2, characterized in that, The functional solvent is one or several of acetone, carbon tetrachloride, N,N-dimethylformamide, cyclohexane, ethanol, ether, dimethyl sulfoxide or tetrahydrofuran.

6. The phase change self-degrading temporary plugging agent according to any one of claims 1 or 2, characterized in that, The water is deionized water or brine with a concentration of 0.5wt% - 5wt%.

7. The phase change self-degrading temporary plugging agent according to any one of claims 1 or 2, characterized in that, The water is one of 5wt% sodium chloride brine, 4wt% sodium chloride brine, 3wt% sodium chloride brine, 2wt% sodium chloride brine, 1wt% sodium chloride brine and 0.5wt% sodium chloride brine.

8. The phase change self-degrading temporary plugging agent according to claim 1, characterized in that, The crosslinking agent is one or more of boric acid, diborinic acid, 3-hydroxybenzeneboronic acid.

9. The phase change self-degrading temporary plugging agent according to claim 1, characterized in that, The functional polymer solid is prepared through the following reaction:

10. A method for preparing a phase change self-degrading temporary plugging agent, characterized in that, Comprising the following steps: S1 Preparation of functional polymer: Stir the monomer small molecule, functional solvent, water and initiator in the formula amount to obtain a functional polymer solution, precipitate the polymer, and dry to obtain the functional polymer solid; S2 Construction of phase change self-degrading temporary plugging agent: Stir the functional polymer solid, functional solvent, water and crosslinking agent in the formula amount to obtain an initial solution of a broad-spectrum temporary plugging agent, then heat for a period of time, and spontaneously form a solution-gel transition based on the reaction of functional groups. Continue to maintain the temperature unchanged, and then heat for another period of time, and the gel self-degrades and breaks into a solution state to obtain the phase change self-degrading temporary plugging agent.

11. The method for preparing a phase change self-degrading temporary plugging agent according to claim 10, characterized in that: In the step S1, it specifically includes: The usage amount of the monomer small molecule, stirring speed, usage amount of water, usage amount of initiator and temperature are limited to enable the polymerization of the monomer small molecule.

12. The method for preparing a phase change self-degrading temporary plugging agent according to claim 10, characterized in that: In the step S1, the temperature is 30°C - 90°C, the stirring speed is 150 - 1100 rpm, and the stirring time is 1.5 - 10 h.

13. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S1, the polymer is precipitated with deionized water.

14. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S2, the stirring speed and stirring time are limited to enable the formation of a homogeneous phase in the corresponding mixed system.

15. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S2, the reaction vessel is a sample bottle, and stirring is carried out by a magnetic stirrer and heating is carried out by an oven.

16. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S2, the stirring speed is 800 - 8000 rpm, and the stirring time is 0.2 - 2 h.

17. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S2, the heating temperature is 45 to 150 °C, and the heating time is 0.5 to 100 h.

18. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein: In the step S2, the reheating time is 8 to 800 h.

19. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 10, wherein, It further includes: S3 Core temporary plugging experiment: Use a core displacement device to conduct a temporary plugging performance test. First, clean the core with a 4 wt% KCl solution, and then dry it at 130 °C. Put the dried core into a core holder, set the temperature to 85 °C, inject the pre-gelled temporary plugging agent solution into the core and let it stand. At regular intervals, test the change in the plugging pressure by injecting a 4 wt% KCl solution; calculate the plugging rate and the unplugging rate of the core based on the pressure change. Among them, the injection rate of all liquids is 6 mL / min.

20. A method for preparing a phase change self-degrading temporary plugging agent as claimed in claim 19, wherein, In the step S3, the core is one of artificial sandstone core, artificial shale core, artificial carbonate rock core, and natural core, and its specification is L×φ = 5.0 cm×2.5 cm.

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